1. HYSTERESIS MOTORS

2. CONTENTS Introduction to hysteresis motor Constructional features
Theory of hysteresis motor
Torque-speed characteristics
Other features of hysteresis motor
Applications
Modeling of hysteresis motor
Summary
References

3. HYSTERESIS MOTOR Synchronous motor with uniform
air gap and without dc excitation.
Starts by virtue of hysteresis &
eddy currents induced in the rotor
by action of rotating mmf of the
stator winding
Operates at synchronous speed.
May operate from 1ø or 3ø supply
Utilizes the phenomenon of
hysteresis to produce mechanical
torque

4. CONSTRUCTIONAL FEATURES
The cylindrical stator structure is identical to that of conventional induction or synchronous motors and is fitted with a three-phase or a single-phase winding, with an auxiliary winding and series capacitor for single-phase operation
Rotor of a hysteresis motor is a smooth solid cylinder of hard steel(that has high hysteresis loss) and does not carry any winding.
It is made of special magnetic material such as magnetically hard cobalt or chrome steel having very large hysteresis loop.

5. THEORY OF HYSTERESIS MOTOR
The axis SS' of the stator m.m.f. wave revolves at synchronous speed, because of hysteresis the magnetization of the rotor lags behind the inducing m.m.f. wave.
The axis RR' of the rotor flux wave lags behind the axis of the stator m.m.f. wave by the hysteresis lag angle "α".
If the rotor is stationary, starting torque is produced proportional to the product of the fundamental components of the stator m.m.f. and rotor flux and the sine of the torque angle " α ".
While the rotor is accelerating, the lag angle " α " remains constant if the flux is constant, since the angle " α " depends merely on the hysteresis loop of the rotor and is independent of the rate at which the loop is traversed.

6. Contd…
Stator magnetic field produces eddy currents in the rotor. They produce their own magnetic field. Thus, there is an additional torque on the rotor due to these eddy currents.
The eddy current loss is given by
pe=kef22B2 where f2 is frequency of eddy currents
Also pe=kes2f12B2 where s is slip and f1 is stator frequency
Hence torque is given by Te=pe/sws
The hysteresis loss is given by
ph=khf2 B1.6
Also ph=khsf1 B1.6
Hence torque is given by Th=ph/sws

7. TORQUE-SPEED CHARACTERISTICS OF HYSTERESIS MOTOR
The motor develops constant torque right up to synchronous speed.
Hysteresis motors can synchronize any load they can accelerate, regardless of the inertia.
After reaching synchronism the motors continue to run at synchronous speed and adjust their torque angle to develop torques required by the loads.
Deviations from the ideal speed torque curves.
*Curve A-when starting torque is not required
*Curve B-when a high starting torque is required.

8. ADDITIONAL FEATURES OF HYSTERESIS MOTOR
It has the ability to pull into synchronization any load that is within its capacity to start and accelerate.
This motor is made in very small sizes only. Hysteresis motors are limited to small size by the difficulty of controlling rotor losses caused by imperfections in the stator mmf wave
The outstanding special feature of a hysteresis motor is the production of nearly constant, ripple-free torque during starting.
With provisions for pole changing in the stator, the motor is multispeed.

9. APPLICATIONS OF HYSTERESIS MOTOR
It has a very low noise level compared to single-phase induction motor because it operates at one speed(synchronous)and its rotor is smooth. With a permanent capacitor stator, hysteresis motor is the smoothest running, quietest single phase motor and is preferred for quality sound reproduction equipments like record players, tape recorders etc
The most common application is for electric clocks and other timing devices
Hysteresis motors are used for rotating gyroscope rotors in inertial navigation and control systems

10. MODELING OF THE HYSTERESIS MOTOR
Hystersis motor basically has the same model as that of PM synchronous motor except that the mode of the rotor is replaced by a nonlinear model of the hysteresis material

11. CIRCUIT MODEL[2]

12. ASSUMPTIONS IN THE MODELING
The magnetic flux is radial in the air gap and tangential in the hysteresis rotor material.
The stator self and mutual inductances are almost independent of the rotor position.
The rotor hysteresis ring is made of cobalt-steel material (as in permanent magnet machines) which has a reasonable electrical resistivity.

13. The voltage and flux linkage equations are
The electromagnetic torque is given by
Te=(3/2)*(P/2)*(λdsiqs-λqsids)

14. SUMMARY
The basic idea about hysteresis motor has been dealt-its constructional features, operation and its applications also.
A circuit model of the hysteresis motor was shown and the modeling of the motor was done.

15. REFERENCES
[1] Omer M. Awed Badeeb “Investigation of the dynamic performance of hysteresis motors using matlab/simulink” . Journal of Electrical Engineering, vol. 56, NO. 3-4, 2005, pp 106–109 [2]H.R.Sourosh,A.R.Rahmati,H.Moghbelli,A.Vahedi,A.Halvaei Niasar “Study on the hunting in high speed hysteresis motors due to the rotor hysteresis material”. IEEE Transactions 2009, pp [3] Ashfaq Husain “Electric Machines” 2003 Dhanpat Rai & Co. (Pvt) Ltd, pp [4] Sheila C Haran “Synchronous Induction and Special Machines” 2001 Scitech Publications(India) Ltd, pp [5] Rex Miller and Mark Richard Miller “Electric Motors” 2004 Wiley dreamtech India Pvt. Ltd, pp

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